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Why Are You Not Supposed to Use Dish Soap To Wash A Car?

So I had a buddy saying he was going to use dish soap to wash his car before he waxed it to strip the paint and I told him not to. He asked why and I couldn't give him a reason not to lol....I've just always heard not to use it. Is it just because it will strip the wax or is there another reason behind it. I got to thinking and I've heard people will recommend using an APC so why not Dawn?

Re: Why Are You Not Supposed to Use Dish Soap To Wash A Car?

Some say because it dries out the rubber trim and requires hot water to completely rinse off. I rinsed my coffee cup once with cold water, won't do that again.

I think that if someone uses it and also uses a conditioner for their trim that no negatives will arise from it. Now on the other hand I wouldn't use automatic dish washer detergent like the neighbor of a guy I recently met did. It etched the clear.

I surely wouldn't use a paint cleaner to wash my dishes is another answer I frequently hear to this question.

Re: Why Are You Not Supposed to Use Dish Soap To Wash A Car?

Originally Posted by tomrzk

So I had a buddy saying he was going to use dish soap to wash his car before he waxed it to strip the paint and I told him not to. He asked why and I couldn't give him a reason not to lol....I've just always heard not to use it. Is it just because it will strip the wax or is there another reason behind it. I got to thinking and I've heard people will recommend using an APC so why not Dawn?

Isn't that the reason he was going to use dish soap, too strip the old wax? He was correct.

Re: Why Are You Not Supposed to Use Dish Soap To Wash A Car?

Dish washing detergents contain allot of degreasers and believe it or not it's needed if you're to get those dinner plates squeaky clean. These chemicals will do the same thing to your cars finish stripping all the wax and protection you spent half the day putting on.

Re: Why Are You Not Supposed to Use Dish Soap To Wash A Car?

I don't know how true this is but I have read that paint is never really completely dry, that there are oils in the paint that keep it healthy and soaps like Dawn with degreasers will pull those oils out of the paint and the paint will not last as long, kind of dry it out making it lose it's shine and depth and creating like what we have seen as clear coat failure. Again I don't know if this is true just something I have read hear on the internet, maybe some paint experts can shed some light on this.

Re: Why Are You Not Supposed to Use Dish Soap To Wash A Car?

Holy crap the wive's tales come out. As Mike Phillips will tell you, old SS paint may be more porous, and therefore can be rejuvenated by "oily" products, but paint has no oil in it to be removed by Dawn. Modern CC paints are catalyzed, and therefore don't really "dry", they cure by a chemical reaction (there may additionally be some carrier solvents, including water, that need to evaporate from the film at the same time curing is occuring).

I am always amused by the Dawn "fears" (you'll wreck your paint! you'll dry out your seals!) The idea that a product that is gentle and safe enough that tens of millions of people put their hands in every day to wash their dishes, eat out of dishes washed in it, is used to clean oil-soaked pelicans and penguins, is somehow too harsh to use on a car, which is designed to perhaps sit out in the elements 24/7, be run through automatic car washes with harsh detergents, and stand up to decon kits (which AG sells) containing caustic and acid steps, simply defies logic.

Re: Why Are You Not Supposed to Use Dish Soap To Wash A Car?

Thanks for dispelling the "old wives tale", I wondered if it was true. I used to always use Dawn and other dish soaps to wash my cars (now they weren't very nice cars) but I never noticed any change in the paint after years of washing like this, and I've always wondered what the difference was between an expensive car wash soap and a mild dish soap.

Re: Why Are You Not Supposed to Use Dish Soap To Wash A Car?

As has been said, Dawn is likely to be less friendly to LSP's. On another forum years ago a member compared the pH (and the ingredients per MSDS) of some car soaps to the evil Dawn and didn't find much difference. I'd be willing to wager that if you you used your regular car soap at the concentration most people use Dawn at for stripping, your car soap wouldn't be too friendly to your LSP, either.

Also, as far as the "seal drying", I'd also be willing to wager that the story behind the people who have observed that went something like this: Detailer shows up to restore old faded car for trade-in. Detailer says "gee, this thing looks terrible, the paint is faded and the trim is all chalky". The owner says "but I washed the car every week!" Detailer asks "with what?", and owner says "with Dawn". Detailer says/thinks "OMG--look how Dawn wrecked this car!"...when the reality is the car sat outside with no wax or trim dressing all its life (or wax and trim dressing removed by Dawn).